Conventionally, an inlet mixer pipe and a diffuser pipe for jet pumps used in boiling water reactors are connected to each other by inserting the inlet mixer pipe into an upper end opening of the diffuser pipe with a clearance left therebetween. This is known as a slip joint structure. The slip joint structure has a clearance which accommodates a structural deformation due to thermal expansion, and acts as an adjusting allowance in connection of members.
The clearance provided in the slip joint structure forms a clearance flow path for coolant through which pumped coolant transferred from the inlet mixer pipe to the diffuser pipe is trying to overflow from the clearance. It is known that when a clearance flow flowing through the clearance flow path reaches a certain flow rate, a vibration having a large amplitude, referred to as self-excited vibration, occurs which may lead to a damage to the jet pump. Note that even in the case of a minute vibration which does not lead to the self-excited vibration, when the minute vibration continues for a long time, e.g., sliding wear of an interconnection portion between a wedge and a riser bracket may cause reduction or loss of support performance of the inlet mixer pipe. Such degradation of the support performance results in an increase of the clearance of the slip joint structure, i.e., an increase in a flow rate of the clearance flow, this eventually increasing possibility of the self-excited vibration.
Conventionally, vibration restraining techniques for jet pumps listed below have been known.
(1) A reinforcing hardware for restraining vibration and wear is provided in an interconnection portion between a wedge and a riser bracket (for example, see Patent Document 1).
(2) A clearance adjuster is provided which eliminates a clearance defined by a riser bracket and an inlet mixer pipe to restrain vibration (for example, see Patent Documents 2 and 3).
(3) A fastener is provided, by which an inlet mixer pipe and a diffuser pipe are press-contacted to each other to restrain vibration (for example, see Patent Document 4).
(4) A member for eliminating a clearance flow is interposed in a clearance between an inlet mixer pipe and a slip joint structure connecting the inlet mixer pipe with a diffuser pipe (see Patent Document 5).    (Patent Document 1) U.S. Pat. No. 6,052,425    (Patent Document 2) Japanese Patent Laid-Open No. 2001-249196    (Patent Document 3) Japanese Patent Laid-Open No. 2003-161795    (Patent Document 4) U.S. Pat. No. 6,394,765    (Patent Document 5) U.S. Pat. No. 6,438,192
Each of the vibration restraining techniques described in Patent Documents 1 to 3 includes a vibration restraining structure at a location away from the connection portion between the inlet mixer pipe and the diffuser pipe. Each of such vibration restraining structures is not intended to directly restrain the self-excited vibration due to the clearance flow described above, so that a restraint effect of the self-excited vibration decreases with distance between the vibration restraining structure and the connection portion between the inlet mixer pipe and the diffuser pipe.
In the vibration restraining technique described in Patent Document 4, the inlet mixer pipe and the diffuser pipe are press-contacted to each other by an external force applied thereto. In the vibration restraining technique described in Patent Document 5, the clearance defined by the inlet mixer pipe and the diffuser pipe is eliminated. Therefore, in each of the vibration restraining techniques, a function of the clearance for accommodating a structural deformation due to e.g. thermal expansion of the inlet mixer or the diffuser pipe is inhibited, as well as mechanical deterioration is caused.
The present invention is made in view of the above circumstances, and has an object to provide a jet pump, and a method for restraining vibration of the jet pump, which can restrain self-excited vibration in a connection portion between an inlet mixer pipe and a diffuser pipe without inhibiting a structural deformation due to thermal expansion and the like.
According to one embodiment, a jet pump disposed in a reactor pressure vessel of a boiling water reactor, the jet pump including an inlet mixer pipe connected to a riser pipe, and a diffuser pipe connected to the inlet mixer pipe to cause a forced circulation of coolant water in the reactor pressure vessel, the jet pump includes: a slip joint structure connecting the inlet mixer pipe and the diffuser pipe to each other by inserting the inlet mixer pipe into an upper end opening of the diffuser pipe with a clearance left therebetween; and a self vibration damping structure configured such that when the clearance defined by an outer pipe wall of the inlet mixer pipe and an inner pipe wall of the diffuser pipe is widening or narrowing due to vibration of the inlet mixer pipe or the diffuser pipe, a flow path resistance inside a clearance flow path for pumped coolant water defined by the clearance is not smaller than a fluid inertia force all over the clearance flow path.
According to another embodiment, a jet pump disposed in a reactor pressure vessel of a boiling water reactor, the jet pump including an inlet mixer pipe connected to a riser pipe, and a diffuser pipe connected to the inlet mixer pipe to cause a forced circulation of coolant water in the reactor pressure vessel, the jet pump includes: a slip joint structure connecting the inlet mixer pipe and the diffuser pipe to each other by inserting the inlet mixer pipe into an upper end opening of the diffuser pipe with a clearance left therebetween; and a self vibration damping structure including a groove portion provided on any one side of an outer pipe wall of the inlet mixer pipe and an inner pipe wall of the diffuser pipe, and a convex portion provided on the other side and being fit into the groove portion with a minute clearance left therebetween.
According to another embodiment, a jet pump disposed in a reactor pressure vessel of a boiling water reactor, the jet pump including an inlet mixer pipe connected to a riser pipe, and a diffuser pipe connected to the inlet mixer pipe to cause a forced circulation of coolant water in the reactor pressure vessel, the jet pump includes: a non-slip joint structure connecting the inlet mixer pipe and the diffuser pipe to each other by abutting an opening edge of the inlet mixer pipe against an opening edge of the diffuser pipe.
According to another embodiment, A method for restraining vibration of a jet pump disposed in a reactor pressure vessel of a boiling water reactor, in which an inlet mixer pipe and a diffuser pipe are connected to each other by inserting the inlet mixer pipe into an upper end opening of the diffuser pipe with a clearance left therebetween, to cause a forced circulation of coolant water in the reactor pressure vessel, the method including: controlling a flow of a clearance flow such that when the clearance defined by an outer pipe wall of the inlet mixer pipe and an inner pipe wall of the diffuser pipe is widening or narrowing due to vibration of the inlet mixer pipe or the diffuser pipe, a flow path resistance inside a clearance flow path for pumped coolant water defined by the clearance is not smaller than a fluid inertia force all over the clearance flow path.
These embodiments of present invention can restrain self-excited vibration in a connection portion between an inlet mixer pipe and a diffuser pipe without inhibiting a structural deformation due to thermal expansion and the like.